1. Field of the Invention
The present invention relates to a measuring apparatus that provides numerical data relative to the linearity of an orientation flat (hereinafter referred to as an Ori-Fla).
2. Description of Related Art
Conventionally, examination of the linearity of an Ori-Fla portion has been by visual methodology, with no provision of quantitative data in which to make judgements. On the other hand, there has been disclosed a wafer Ori-Fla positioning method in which an Ori-Fla is positioned by pressing a wafer against a positioning mechanism provided on a wafer chuck mounting surface (Unexamined Japanese Patent Publication No. 10-22368). In this positioning method, the wafer chuck mounting surface is provided so as to be inclined, and a gas flow for floating a wafer with respect to a wafer chuck is generated by air blowing means.
In the positioning method configured as described above, when air is blown from the air blowing means in a state in which a wafer is mounted on the wafer chuck mounting surface, the wafer moves smoothly under gravity toward a positioning mechanism along the inclination of the wafer chuck mounting surface. As a result, the positioning of the Ori-Fla can be performed reliably.
Further, there has been disclosed an exposure device that has a stage, a rough positioning mechanism, and number detecting means, and can perform exact rough positioning of a wafer without pattern at the time of first-level pattern exposure (Unexamined Japanese Patent Publication No. 8-78316). In this exposure device, at least three stopper members are provided to roughly position a wafer on the stage, and the stage moves in the longitudinal and transverse X & Y directions and in the rotation direction of θ. Also, the rough positioning mechanism performs rough positioning by causing the peripheral portions of wafer mounted on the stage to abut against the stopper members. Further, the number detecting means detects an identification number scribed on the wafer positioned roughly so that the wafer moves on the stage until the identification number arrives at a predetermined position.
In the conventional method in which the linearity of the Ori-Fla portion is examined visually, however, the acceptability or non-acceptability of linearity cannot be determined quantitatively. Also, in the conventional Ori-Fla positioning method disclosed in the aforementioned Unexamined Japanese Patent Publication No. 10-22368, or in the exposure device disclosed in Unexamined Japanese Patent Publication No. 8-78316, the fabrication accuracy of the Ori-Fla, especially the fabrication accuracy in chamfering the Ori-Fla is poor because the linearity of the Ori-Fla of wafer itself is not measured. For example, when as shown in FIG. 8(a), a vertex P is formed at the center of an Ori-Fla 8a, and the Ori-Fla 8a is formed of a first side 8b and a second side 8c on opposite sides of the vertex P, there arises a problem in that the crystalline orientation of a wafer 8 deflects comparing the time when the first side 8b is aligned with the positioning mechanism with the time when the second side 8c is aligned with the positioning mechanism. Further, the Ori-Fla 8a of the wafer 8 as shown in FIG. 8(b) also presents the same problem. With an extremely high level of human expertise, judgements can be made visually if the maximum allowable value of the Ori-Fla linearity is ≧25 μm, if the maximum allowable linearity value of the Ori-Fla is <25 μm, there arises a problem in that it is nearly impossible to determine the measurement visually.